Field of the Invention
The invention relates in general to a device and method for a communication system, and more particularly to a device and method for handling bit allocation.
Description of the Related Art
Orthogonal frequency-division multiplexing (OFDM) (or referred to as discrete multi-tone modulation (DMT)) technologies have high spectrum utilization efficiency and strong attenuation resistance capabilities. Thus, many modern high-speed communication systems adopt OFDM technologies to transmit and receive signals, in order to increase the probability of correctly recovering the signals. In OFDM technologies, various numbers of bits can be allocated to individual subcarriers to thoroughly use the capacity of channels. Bit allocation of the subcarriers may be recorded in a tonemap. In general, the tonemap includes carrier-dependent information, such as the bit numbers carried by the individual subcarriers of OFDM signals, and so a communication device can transmit/receive bits on these subcarriers according to the tonemap.
A communication device may determine the bit number of a subcarrier according to the channel quality, i.e., calculating the bit allocation of the subcarrier according to the channel quality. However, in actual operations of a communication system, the communication device may be incapable of transmitting or receiving signals according to the bit allocation that is determined by the above method. For example, a communication service provider may be restrained from transmitting OFDM signals, or the number of physical blocks (PB) included in OFDM symbols is limited. Under such circumstances, the communication device needs to modify the original bit allocation, so as to transmit or receive OFDM signals while meeting the limitation.
The bit allocation that is determined according to the channel quality usually causes the communication device to have optimal performance, such as highest throughput, and arbitrarily modifying the bit allocation may cause performance degradation. Therefore, there is a need for a solution that modifies the bit allocation while meeting limitations and reducing the impact on the performance.